Over the past decade, one dimensional (1D) semiconductor nanostructures, such as nanotubes and nanowires, have attracted special attention due to their high aspect and surface to volume ratios, small radius of their tips, absence of three dimensional (3D) growth related defects, such as threading dislocations, and fundamentally new electronic properties resulting from quantum confinement. These nanostructures can be used as building blocks for future nanoscale electronic devices and nanoelectromechanical systems (NEMS), designed using a bottom-up approach. A variety of 1D nanowires of Si, ZnO, SiC and other semiconductors have been synthesized.
Taking SiC as an example, SiC offers opportunities in fabricating nanoelectronic devices and NEMS for chemical/biochemical sensing, high-temperature, high-frequency and aggressive environment applications. These opportunities are due to wide bandgap, high electric breakdown field, mechanical robust, chemical inertness and biocompatibility.
However, before any of the above-mentioned applications could be realized, a reliable technique for the high yield, cost effective fabrication of SiC nanostructures with controlled morphology (size, shape, location, and orientation), structure (polytype and defects) and electronic properties (doping level and transport) needs to be developed. Currently, post-growth processing and manipulation of nanostructures is an extremely difficult task.
Several known techniques have been applied to synthesize SiC nanowires using physical evaporation, chemical vapor deposition, laser ablation, direct chemical reaction, etc. However, such existing growth methods for synthesis of SiC nanostructures exhibit several problems and limitations. First, all of the existing methods can grow only 3C—SiC polytype nanowires, while methods for selective growth of other polytype, such as hexagonal 4H and 6H—SiC nanowires, have not yet been developed. It is known that the hexagonal SiC polytypes have many advantageous properties over 3C—SiC, such as larger bandgap, lower intrinsic carrier concentration, higher hole mobility and higher breakdown voltage, etc. The lack of the ability to fabricate hexagonal SiC polytype nanowires is a significant draw back for the use of SiC nanowires in many important applications.
Second, the growth of SiC nanostructures using the above-mentioned conventional methods is very slow (in the μm range per hour), and the morphology of the SiC nanostructures are uncontrollable. Different sizes and shapes of nanostructures, such as nanowires, nanoribbons, nanosaws and two dimensional (2D) or 3D features, are often present in the same sample. Consequently, the 1D nanostructures with desired morphologies and properties constitute just a fraction of the total yield. The slow growth rate and low yield of desired nanostructures become critical technical barriers for the practical applications of the existing growth methods in terms of large quantity and low-cost fabrication of SiC nanostructures.
Consequently, what is needed is a simpler and more effective technique to overcome the above mentioned technical barriers in order to open the doors for high-yield, cost-effective growth of nanowires (e.g., SiC nanowires, etc.) with selected polytype, morphology, and properties.